Avian radars are used to track birds in flight in the vicinity of airfields, wind farms, communications towers, oil and mining operations, and along migration routes. Birds are a significant hazard to aviation safety. Applications that require bird monitoring are the bird aircraft strike hazard (BASH) management problem and the natural resource management (NRM) problem. Billions of dollars in damage to aircraft and significant loss of life have been recorded due to birds flying into aircraft, particularly during take-off and landing in the vicinity of airports.
The danger associated with birds depends on their altitude (among other factors). End-users of bird detection and tracking radars need to know the 3D locations (i.e. latitudes, longitudes and altitudes) of tracked birds. State-of-the-art avian radars provide target tracking only within a slice of the 3D surveillance volume and with high-resolution localization only in two dimensions.
As with any instrumentation that continuously collects data, digital avian radars generate large volumes of information. To be beneficial, those data must be analyzed and presented in a manner that is relevant to the end-user. The three-dimensional locations of the targets are one of the most important pieces of information obtained from avian radar tracks. The more accurate and precise the data, the more useful they are. Location is of obvious importance to accurately track the position of the bird over the terrain. Altitude is important for determining whether the bird is at an altitude such that it poses a threat to aircraft in flight.
In order to try and assess bird behavior, wildlife managers and ornithologists visually monitor birds. They identify and count birds at various locations and times of day, and may also note additional information such as the species, flight pattern, altitude, etc. Because of limited resources, these counts tend to be sparse in both their spatial and temporal aspects. Because of the sparseness, the attempted assessment of general bird behavior lacks critical information.
State-of-the-art avian radars use inexpensive, commercial-off-the-shelf (COTS) X-band (or S-band) marine radar transceivers, fitted with slotted-waveguide array antennas, as well as parabolic reflector or Cassegrain (dish) antennas. The raw received baseband signals are digitized, followed by detection, tracking and display of bird targets. State-of-the-art avian radars provide continuous, day or night, all-weather, situational awareness with automated detection, localization and warnings of hazards within the small slice of the 3D surveillance volume they monitor. They provide high-quality, real-time target track data with sophisticated criteria to determine potentially dangerous target behavior, as well as communication of real-time alerts to end-users who require that information. They also minimize operator interaction and in-the-loop requirements.
State-of-the-art avian radars features include:                Low-cost, high-performance radar antennas and transceivers mounted on ground-based pedestals        Radar processing that can reliably detect and track small maneuvering targets in dense target and clutter environments        Real-time display of target tracks in a geographic framework        Automatic hazard detection and alert capability to remote end-users        The formation of radar networks to provide wide-area coverage        Low cost of operation        Low life cycle costs        Data and analysis support for research and development        
COTS marine radars are very inexpensive. These marine radars exhibit surprisingly good hardware specifications. However, as-is, these radars deliver mediocre performance for bird targets because of their primitive signal processing, which is only required to detect marine vessels and land-masses. Combining a COTS marine radar with a digitizer board and a software radar processor that runs on a COTS personal computer (PC) and a parabolic dish antenna forms a state-of-the-art avian radar, but one with a very limited three-dimensional (3D) localization capability.
Slotted-waveguide array antennas are used to provide two-dimensional (2D) localization (i.e. range and azimuth, which can be translated to latitude and longitude). These systems provide good volume coverage due to the typically larger vertical (elevation) beamwidth, which is on the order of 20 degrees. Such systems, however, cannot provide useful altitude estimates of tracked targets when the radar is spinning horizontally in its usual orientation. This is because the beam uncertainty in the 3rd dimension (elevation), which is on the order of the beam extent (up to 20 degrees), is too large. For example, the elevation beam extent or altitude uncertainty for a target at a distance of just 1 km from the radar is about 1,000 feet. This means that if both a plane and a bird are being tracked by the radar at a distance of 1 km away, the radar cannot tell whether the two targets are 1,000 feet apart (i.e. one is near the ground and the other is at the upper edge of the vertical beam, 1,000 feet off the ground) or whether they are at the same altitude where a collision could occur. While some radar configurations orient the slotted-array antenna so that it spins vertically (rather than horizontally) to get a measure of altitude, see Nocturnal Bird Migration over an Appalachian Ridge at a Proposed Wind Power Project, Mabee et al, Wildlife Society Bulletin 34(3), 2006, page 683, they still can only operate as 2D radars. In order to measure altitude, radars in this configuration can no longer provide 360-degree azimuthal coverage (which a conventional azimuth-rotating radar provides).
Parabolic reflector or Cassegrain (dish) antennas are used today to provide a very limited 3D localization capability. These antennas employ a single beam (pencil shaped), fixed in elevation, but rotating in azimuth. The azimuth rotation results in the usual 2D, 360-degree coverage with localization in range-azimuth or latitude-longitude. However, by using a narrow pencil beam (say between 2 and 4 degrees wide), the altitude uncertainty reduces significantly as compared to the 20 deg slotted-array antenna. Using the previous example, with targets at a distance of 1 km from the radar and a 4-degree dish antenna, altitude estimates with uncertainties on the order of 200 feet are now possible. While providing useful altitude information at very short ranges, the altitude estimates are still of limited use at further ranges. Also, volume coverage is restricted accordingly with the narrower pencil beam.
Merrill I. Skolnik in his Introduction to Radar Systems, 2nd Edition, McGraw-Hill Book Company 1980 and his Radar Handbook, 2nd Edition, McGraw-Hill, Inc., 1990, describes altitude-finding radars that use nodding horizontal fan beams. These radars are steered to the bearing where targets have been detected by an independent 2D air-surveillance radar. These altitude-finding radars cannot get altitude estimates for more than 20 or so targets per minute, and have problems with azimuth-elevation (Az-El) ambiguities in dense target environments. Military airborne and land-based tracking radars provide altitude information for a single target only (via closed-loop steering in both dimensions). They use monopulse or sequential lobing techniques to obtain the off-boresight error signals, but like the altitude-finding radars, are unable to perform 3D surveillance. Military 3D surveillance radars, on the other hand, employ rotating phased array antennas that form either multiple receive beams or rapidly electronic-scanning pencil beams. See Radar Applications, Merrill I. Skolnik, IEEE Press New York, 1987.
State-of-the-art weather radars use a helical scanning strategy. These radars form a 3D “image” of the rain intensity in each volume element. Weather radar resolution capabilities (in both time and space) are not suitable for tracking birds.
Weather radar presents density of water in the birds as measured by reflectivity. This reflectivity can be quantified into migration traffic rates (see S. A. Gauthreaux and C. G. Belser, 1998. “Displays of Bird Movements on the WSR-88D: Patterns and Quantification”, Weather and Forecasting 13: 453-464). With its most detailed data, weather radar can give an overview of the density of migrants taking off on migration from localized areas which can be correlated with habitat as described by S. A. Gauthreaux and C. G. Belser, 2005, “Radar Ornithology and the Conservation of Migratory Birds” USDA Forest Service Gen. Tech. Rep. PSW-GTR-191. However, even at its best resolution, it cannot track individual migrants.
Avian radars detect and track individual avian targets. In state-of-the-art avian radars, the numbers of targets are estimated based on reflectivity. The altitudinal distribution of birds is not achievable with the WSR-88D data without access to the data from individual scans. Even with data from individual scans the number of birds is inferred based on reflectivity. The avian targets tracked by current avian radars can be resolved into single birds or groups based on radar cross-section.
U.S. Pat. No. 7,864,103 entitled “Device and Method for 3D Avian Height-Finding Radar” is incorporated herein by reference. The radar systems and methods described therein are azimuth scanning systems with means of varying an elevation pointing angle. Those radar systems and methods are 3D surveillance volume scanning radars. The systems described in U.S. Pat. No. 7,864,103 include radars with multiple beams, slow elevation scanners, and multiple radars, and cover a 3D surveillance volume.
U.S. Pat. No. 7,940,206 entitled “Low-Cost, High-Performance Radar Networks” is also incorporated herein by reference. The radar systems and methods described therein include at least one radar with a computer on a network that tracks targets and sends target data to a radar data server with a database to store and provide data for real-time and historical access and connected to users via an interface. The systems can include detection, clutter suppression, MHT/IMM (multiple hypothesis tracking/interacting multiple models), PPI (plan position indicator) displays, real-time target displays on background map, multiple radars, remote control and operation, unattended monitoring with alerts, user-applications that integrate data from the database (e.g. real-time data into a common operating picture (COP) tactical display), multi-sensor fusion, low RCS targets including birds and aircraft, COTS marine radars, COTS computers, SQL databases, SIMD (serial instruction multiple data) programming, software-configurable processors, web servers providing data to user client applications for accessing past and live data, and track data including range, azimuth, lat, long, altitude, intensity, heading, speed, echo size, date/time.